A wind turbine, such as a Horizontal Axis Wind Turbine, for generating electrical power has a tower that support a nacelle at its top end. A rotor extends from the nacelle and has turbine blades. During operation, prevailing winds cause the turbine blades to rotate the rotor, which is coupled to a generator within the nacelle to produce electricity. To orient the blades, the nacelle can turn about the vertical axis of the tower.
The tower can be any acceptable height. However, the power generation capacity of a wind turbine is directly related to how long the turbine blades are. The length of the turbine blades in turn dictates the required height of the tower. In some large-scale installations, the blades can be about 45-meters long, and the tower can be as much as 90-meters high. Generally, the tower tapers from its base to its top end, which still provides the required strength but with reduced material and fabrication costs. Due to their overall height, the tower is manufactured and transported in a number of tower sections that assemble together at the installation site.
As will be appreciated, the different components of the wind turbine are separately manufactured, sometimes at different locations, and are then transported in pieces to the desired site where they are assembled. Because the components are manufactured in many different places, a number of various forms of transportation must be used, including ships, barges, trains, and trucks.
The sheer size of the various components complicates the transportation. Additionally, the components must be protected and handled properly during transportation to prevent damage. Moreover, the components in many cases must be switched from one mode of transport to another mode during stages of the journey. In the end, it will be appreciated that the logistics to move the various components from the point of manufacture to the ultimate installation site can be complicated, expensive, and time consuming.
Each mode of transport presents challenges to transporting the tower sections. In particular, the profile for railroad transport can be tightly limited because the trains must traverse curved sections and complex rail yards. Mounting fixtures are used to fix the tower sections to railcars during transport.
A particular example of mounting fixtures for fixing tower sections is disclosed in U.S. Pat. No. 8,529,174. Reproduced here in FIG. 1, a train 2 is shown for transporting a three-section tower assembly via rail 1 according to the prior art. The train 2 has three railroad flatcars 4, 6, and 8 traversing the rail 1, and the tower assembly has three tower sections, which include a base tower section 12, a middle tower section 14, and a top tower section 10—each tapering from the base to the top. The base tower section 12 is loaded onto a center flatcar 6 and is disposed toward one end of the flatcar 6, clearing an open area at the opposite end of the flatcar 6. The middle tower section 14 is loaded onto another flatcar 8 and has a length that takes up most of the length of the flatcar 8. The top tower section 10 is loaded onto yet another flatcar 4. The length of the top tower section 10 is longer than the length of the flatcar 4 so that one end of the section 10 extends over the next coupled flatcar 6.
Each of the tower sections 10, 12, 14 is supported on the flatcars 4, 6, and 8 using saddle assemblies. Looking in particular at how the middle tower section 14 is supported on the flatcar 8, reference is directed to FIG. 2A. The flatcar 8 is a conventional 90-foot flatcar with a pair of conventional bolsters 48, 50, and a load deck 11. In this example, the tower section 14 has a length approximately as long as the flatcar's deck 11. The middle tower section 14 includes an internal flange 30 on its larger circumference end for engaging the base tower section (12) when the tower is finally assembled. The flange 30 is also used as an attachment point for a stop 34 disposed between the flatcar's deck 11 and the tower section 14 during transit. The stop 34 retains the tower section 14 against longitudinal movement with respect to the flatcar 8. To a lesser extent, the stop 34 also retains the tower section 14 against lateral movement.
The primary lateral support is by saddles assemblies 38, 42. The weight of the tower section 14 is supported by a first saddle assembly 38 located over the bolster 48, and a second saddle assembly 42 located over the other bolster 50. The second saddle assembly 42 also includes a spacer assembly 44.
The sectional view of FIG. 2B is taken at the location of the flange 30 on the end of tower section 14. Plural connecting bolts join the flange 30 to the stop 34, which has previously been fixed to the deck 11, such as by welding or other suitable means. As illustrated, the stop 34 is comprised of an attachment plate bolted to the flange 30, and of plural gusset plates welded to the attachment plate and the deck 11 of the flatcar 8.
The sectional view of FIG. 2C is taken at the position of the bolster 48 of the flatcar 8 where the saddle assembly 38 is situated. The saddle assembly 38 is fixed to the deck 11 of the flatcar 14. The upper surface of the saddle assembly 38 is a saddle that conforms to the shape of the tower section 14 at a location along the elongated portion of the tower section 14 at which the saddles assembly 38 engages. Because the tower 14 is circular in cross-section, the saddle assembly 38 is an arcuate circular section, conforming to the exterior shape of the tower section 14. A resilient saddle liner 40 is disposed between saddle assembly 38 and the surface of the tower section 14 to protect the surface finish of the tower section 14 and to accommodate small variances between the two surface shapes.
The sectional view of FIG. 2D is taken at the location of the other bolster 50, which is also the location of the other saddle assembly 42. This saddle assembly 42 is substantially the same as the other saddle assembly 38. To accommodate different sizes and shapes of the tower cross sections, a spacer assembly 44 is positioned on top of saddle assembly 42 and adapts the conformal shape of the saddle assembly 42 to the exterior shape of the tower section 14 at the location of support of saddle assembly 42. Because the tower section 14 has a smaller diameter at the location of saddle assembly 42, the spacer assembly 44 presents a correspondingly smaller diameter spacer saddle profile. A resilient liner 46 is disposed between the spacer assembly saddle 44 and the tower 14. Also, the saddle assembly 42 is fixed to the deck 11 of the flatcar 8 using pins disposed between fixed deck brackets and gussets on the saddle assembly.
Although current techniques are available for transporting tower sections on a railcar, such as disclosed in U.S. Pat. No. 8,529,174, transportation personnel are continually seeking more versatile and useful ways to transport large cylindrical objects, such as tower sections of a wind turbine.